Wireless communication terminal and wireless communication method for multi-user uplink transmission

ABSTRACT

The present invention relates to a wireless communication terminal and a wireless communication method for efficiently scheduling multi-user uplink transmission. 
     To this end, provided are a wireless communication terminal, including: a transceiver; and a processor, wherein the processor is configured to: receive, by the transceiver, a trigger frame that triggers a multi-user uplink transmission, perform a multi-user uplink transmission in response to the received trigger frame, and receive, by the transceiver, an ACK for the multi-user uplink transmission, wherein when the multi-user uplink transmission is performed on a resource unit in which a temporary association identifier (AID) is assigned by the received trigger frame, the processor obtains ACK information for the terminal from the ACK for the multi-user uplink transmission based on the temporary AID and a wireless communication method using the same.

TECHNICAL FIELD

The present invention relates to a wireless communication terminal and awireless communication method for multi-user uplink transmission, andmore particularly, to a wireless communication terminal and a wirelesscommunication method for efficiently scheduling simultaneous uplinktransmission of a plurality of terminals.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of awireless interface accepted by 802.11n, such as a wider wirelessfrequency bandwidth (a maximum of 160 MHz), more MIMO spatial streams (amaximum of 8), multi-user MIMO, and high-density modulation (a maximumof 256 QAM). Further, as a scheme that transmits data by using a 60 GHzband instead of the existing 2.4 GHz/5 GHz, IEEE 802.11ad has beenprovided. The IEEE 802.11ad is a transmission standard that provides aspeed of a maximum of 7 Gbps by using a beamforming technology and issuitable for high bit rate moving picture streaming such as massive dataor non-compression HD video. However, since it is difficult for the 60GHz frequency band to pass through an obstacle, it is disadvantageous inthat the 60 GHz frequency band can be used only among devices in ashort-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

DISCLOSURE Technical Problem

The present invention has an object to providehigh-efficiency/high-performance wireless LAN communication in ahigh-density environment as described above.

In addition, the present invention has an object to provide a method bywhich a plurality of terminals can efficiently perform multi-user uplinktransmission.

In addition, the present invention has an object to provide a structureof a trigger frame for a multi-user uplink transmission in acontention-based channel access system.

Technical Solution

In order to achieve the objects, the present invention provides awireless communication method and a wireless communication terminal asbelow.

First, an exemplary embodiment of the present invention provides awireless communication terminal, including: a transceiver configured totransmit and receive a wireless signal; and a processor configured tocontrol an operation of the wireless communication terminal, wherein thetransceiver receives a trigger frame that triggers a multi-user uplinkdata transmission, transmits multi-user uplink data in response to thereceived trigger frame and receives a block ACK in response to themulti-user uplink data, and wherein the processor obtains a temporaryassociation identifier (AID) from the received trigger frame and obtainsACK information for the terminal in the block ACK based on the temporaryAID.

In this case, the temporary AID may indicate a resource unit containingACK information for the terminal in the block ACK.

According to an embodiment, the temporary AID may be a group AIDcorresponding to a plurality of STAs performing the multi-user uplinkdata transmission.

According to another embodiment, the temporary AID may be selected fromunused AIDs in a corresponding basic service set (BSS).

According to a first embodiment, the AID may comprise a first AID setconsisting of AIDs used for AID assignment of terminals and a second AIDset consisting of AIDs not used for AID assignment of terminals, and thetemporary AID may be selected from the second AID set.

According to a second embodiment, the AID may comprise a first AID setconsisting of AIDs used for AID assignment of terminals and a second AIDset consisting of AIDs not used for AID assignment of terminals, and thetemporary AID may be selected from unused AIDs of the first AID set.

Furthermore, the temporary AID may have a value different from the AIDassigned to the terminal.

In addition, the trigger frame may set at least one random accessresource unit, and the temporary AID may be assigned to the randomaccess resource unit.

According to an embodiment, the block ACK may be a multi-STA block ACK(M-BA), and the temporary AID may be included in a per STA informationfield of the M-BA.

According to another embodiment, the block ACK may be an OFDMA blockACK, and the temporary AID may be included in HE-SIG-B of the OFDMAblock ACK.

In addition, an exemplary embodiment of the present invention provides awireless communication method of a wireless communication terminal,including: receiving a trigger frame that triggers a multi-user uplinkdata transmission; obtaining a temporary association identifier (AID)from the received trigger frame; transmitting multi-user uplink data inresponse to the received trigger frame; receiving a block ACK inresponse to the multi-user uplink data; and obtaining ACK informationfor the terminal in the block ACK based on the temporary AID.

Advantageous Effects

According to an embodiment of the present invention, efficientmulti-user uplink transmission scheduling is possible in acontention-based channel access system.

According to an embodiment of the present invention, it is possible toefficiently support random access of terminals using a trigger frame.

Also, according to an embodiment of the present invention, it ispossible to efficiently set NAVs for terminals not participating in themulti-user uplink/downlink transmission.

According to an embodiment of the present invention, it is possible toincrease the total resource utilization rate in the contention-basedchannel access system and improve the performance of the wireless LANsystem.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a wireless LAN system according to an embodiment ofthe present invention.

FIG. 2 illustrates a wireless LAN system according to another embodimentof the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 schematically illustrates a process in which a STA and an AP seta link.

FIG. 6 illustrates a carrier sense multiple access (CSMA)/collisionavoidance (CA) method used in wireless LAN communication.

FIG. 7 illustrates a method for performing a distributed coordinationfunction (DCF) using a request to send (RTS) frame and a clear to send(CTS) frame.

FIGS. 8 and 9 illustrate a hidden node protection method in a multi-usertransmission process.

FIG. 10 illustrates a structure of a trigger frame according to anembodiment of the present invention.

FIG. 11 illustrates a configuration of a resource unit pattern accordingto an embodiment of the present invention.

FIG. 12 illustrates a configuration of a resource unit pattern accordingto another embodiment of the present invention.

FIG. 13 illustrates a structure of a common information field of atrigger frame according to another embodiment of the present invention.

FIG. 14 illustrates a structure of a trigger frame and a resource unitpattern according to an embodiment of the present invention.

FIG. 15 illustrates a resource allocation method for a random accessbased multi-user uplink transmission according to an embodiment of thepresent invention.

FIG. 16 illustrates a resource allocation method for a random accessbased multi-user uplink transmission according to another embodiment ofthe present invention.

FIGS. 17 and 18 illustrate a method for multi-user uplink transmissionusing a temporary AID assignment method according to the above-describedembodiments.

FIG. 19 illustrates a method of controlling a random access basedmulti-user uplink transmission according to a further embodiment of thepresent invention.

FIG. 20 illustrates a buffer status reporting method using a randomaccess based multi-user uplink transmission according to an embodimentof the present invention.

FIG. 21 illustrates a buffer status reporting method using a randomaccess based multi-user uplink transmission according to anotherembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Terms used in the specification adopt general terms which are currentlywidely used by considering functions in the present invention, but theterms may be changed depending on an intention of those skilled in theart, customs, and emergence of new technology. Further, in a specificcase, there is a term arbitrarily selected by an applicant and in thiscase, a meaning thereof will be described in a corresponding descriptionpart of the invention. Accordingly, it should be revealed that a termused in the specification should be analyzed based on not just a name ofthe term but a substantial meaning of the term and contents throughoutthe specification.

Throughout this specification and the claims that follow, when it isdescribed that an element is “coupled” to another element, the elementmay be “directly coupled” to the other element or “electrically coupled”to the other element through a third element. Further, unless explicitlydescribed to the contrary, the word “comprise” and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof stated elements but not the exclusion of any other elements.Moreover, limitations such as “or more” or “or less” based on a specificthreshold may be appropriately substituted with “more than” or “lessthan”, respectively.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2015-0068159, 10-2015-0126196 and 10-2015-0156149filed in the Korean Intellectual Property Office and the embodiments andmentioned items described in the respective application, which forms thebasis of the priority, shall be included in the Detailed Description ofthe present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a wireless medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a non-AP STA, or an AP, or to both terms. A station forwireless communication includes a processor and a transceiver andaccording to the embodiment, may further include a user interface unitand a display unit. The processor may generate a frame to be transmittedthrough a wireless network or process a frame received through thewireless network and besides, perform various processing for controllingthe station. In addition, the transceiver is functionally connected withthe processor and transmits and receives frames through the wirelessnetwork for the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense. In the present invention, an AP may also be referredto as a base wireless communication terminal. The base wirelesscommunication terminal may be used as a term which includes an AP, abase station, an eNB (i.e. eNodeB) and a transmission point (TP) in abroad sense. In addition, the base wireless communication terminal mayinclude various types of wireless communication terminals that allocatemedium resources and perform scheduling in communication with aplurality of wireless communication terminals.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a wireless signal suchas a wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. That is, the processor 110 may be a modem or amodulator/demodulator for modulating and demodulating wireless signalstransmitted to and received from the transceiver 120. The processor 110controls various operations of wireless signal transmission/reception ofthe station 100 according to the embodiment of the present invention. Adetailed embodiment thereof will be described below.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. According to an embodiment, the processor210 may be a modem or a modulator/demodulator for modulating anddemodulating wireless signals transmitted to and received from thetransceiver 220. The processor 210 controls various operations such aswireless signal transmission/reception of the AP 200 according to theembodiment of the present invention. A detailed embodiment thereof willbe described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b). In this specification, an association basically means awireless association, but the present invention is not limited thereto,and the association may include both the wireless association and awired association in a broad sense.

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

FIG. 6 is a diagram illustrating a carrier sense multiple access(CSMA)/collision avoidance (CA) method used in wireless LANcommunication.

A terminal that performs a wireless LAN communication checks whether achannel is busy by performing carrier sensing before transmitting data.When a wireless signal having a predetermined strength or more issensed, it is determined that the corresponding channel is busy and theterminal delays the access to the corresponding channel. Such a processis referred to as clear channel assessment (CCA) and a level to decidewhether the corresponding signal is sensed is referred to as a CCAthreshold. When a wireless signal having the CCA threshold or more,which is received by the terminal, indicates the corresponding terminalas a receiver, the terminal processes the received wireless signal.Meanwhile, when a wireless signal is not sensed in the correspondingchannel or a wireless signal having a strength smaller than the CCAthreshold is sensed, it is determined that the channel is idle.

When it is determined that the channel is idle, each terminal havingdata to be transmitted performs a backoff procedure after an interframespace (IFS) time depending on a situation of each terminal, forinstance, an arbitration IFS (AIFS), a PCF IFS (PIFS), or the likeelapses. According to the embodiment, the AIFS may be used as acomponent which substitutes for the existing DCF IFS (DIFS). Eachterminal stands by while decreasing slot time(s) as long as a randomnumber assigned to the corresponding terminal during an interval of anidle state of the channel and a terminal that completely exhausts theslot time(s) attempts to access the corresponding channel. As such, aninterval in which each terminal performs the backoff procedure isreferred to as a contention window interval.

When a specific terminal successfully accesses the channel, thecorresponding terminal may transmit data through the channel. However,when the terminal which attempts the access collides with anotherterminal, the terminals which collide with each other are assigned withnew random numbers, respectively to perform the backoff procedure again.According to an embodiment, a random number newly assigned to eachterminal may be decided within a range (2*CW) which is twice larger thana range (a contention window, CW) of a random number which thecorresponding terminal is previously assigned. Meanwhile, each terminalattempts the access by performing the backoff procedure again in a nextcontention window interval and in this case, each terminal performs thebackoff procedure from slot time(s) which remained in the previouscontention window interval. By such a method, the respective terminalsthat perform the wireless LAN communication may avoid a mutual collisionfor a specific channel.

FIG. 7 is a diagram illustrating a method for performing a distributedcoordination function using a request to send (RTS) frame and a clear tosend (CTS) frame.

The AP and STAs in the BSS contend in order to obtain an authority fortransmitting data. When data transmission at the previous step iscompleted, each terminal having data to be transmitted performs abackoff procedure while decreasing a backoff counter (alternatively, abackoff timer) of a random number allocated to each terminal after anAFIS time. A transmitting terminal in which the backoff counter expirestransmits the request to send (RTS) frame to notify that correspondingterminal has data to transmit. According to an exemplary embodiment ofFIG. 7, STA1 which holds a lead in contention with minimum backoff maytransmit the RTS frame after the backoff counter expires. The RTS frameincludes information on a receiver address, a transmitter address, andduration. A receiving terminal (i.e., the AP in FIG. 7) that receivesthe RTS frame transmits the clear to send (CTS) frame after waiting fora short IFS (SIFS) time to notify that the data transmission isavailable to the transmitting terminal STA1. The CTS frame includes theinformation on a receiver address and duration. In this case, thereceiver address of the CTS frame may be set identically to atransmitter address of the RTS frame corresponding thereto, that is, anaddress of the transmitting terminal STA1.

The transmitting terminal STA1 that receives the CTS frame transmits thedata after a SIFS time. When the data transmission is completed, thereceiving terminal AP transmits an acknowledgment (ACK) frame after aSIFS time to notify that the data transmission is completed. When thetransmitting terminal receives the ACK frame within a predeterminedtime, the transmitting terminal regards that the data transmission issuccessful. However, when the transmitting terminal does not receive theACK frame within the predetermined time, the transmitting terminalregards that the data transmission is failed. Meanwhile, adjacentterminals that receive at least one of the RTS frame and the CTS framein the course of the transmission procedure set a network allocationvector (NAV) and do not perform data transmission until the set NAV isterminated. In this case, the NAV of each terminal may be set based on aduration field of the received RTS frame or CTS frame.

In the course of the aforementioned data transmission procedure, whenthe RTS frame or CTS frame of the terminals is not normally transferredto a target terminal (i.e., a terminal of the receiver address) due to asituation such as interference or a collision, a subsequent process issuspended. The transmitting terminal STA1 that transmitted the RTS frameregards that the data transmission is unavailable and participates in anext contention by being allocated with a new random number. In thiscase, the newly allocated random number may be determined within a range(2*CW) twice larger than a previous predetermined random number range (acontention window, CW).

Multi-User Uplink Transmission

When using orthogonal frequency division multiple access (OFDMA) ormulti-input multi-output (MIMO), one wireless communication terminal cansimultaneously transmit data to a plurality of wireless communicationterminals. Further, one wireless communication terminal cansimultaneously receive data from a plurality of wireless communicationterminals. For example, a multi-user downlink transmission in which anAP simultaneously transmits data to a plurality of STAs, and amulti-user uplink transmission in which a plurality of STAssimultaneously transmit data to the AP may be performed.

In order to perform the multi-user uplink transmission, the channel tobe used and the transmission start time of each STA that performs uplinktransmission should be adjusted. In order to efficiently schedule themulti-user uplink transmission, state information of each STA needs tobe transmitted to the AP. According to an embodiment of the presentinvention, information for scheduling of a multi-user uplinktransmission may be indicated through a predetermined field of apreamble of a packet and/or a predetermined field of a MAC header. Forexample, a STA may indicate information for multi-user uplinktransmission scheduling through a predetermined field of a preamble or aMAC header of an uplink transmission packet, and may transmit theinformation to an AP. In this case, the information for multi-useruplink transmission scheduling includes at least one of buffer statusinformation of each STA, channel state information measured by each STA.The buffer status information of the STA may indicate at least one ofwhether the STA has uplink data to be transmitted, the access category(AC) of the uplink data and the size (or the transmission time) of theuplink data.

According to an embodiment of the present invention, the multi-useruplink transmission process may be managed by the AP. The multi-useruplink transmission may be performed in response to a trigger frametransmitted by the AP. The STAs simultaneously transmit uplink data apredetermined IFS time after receiving the trigger frame. The triggerframe indicates the data transmission time point of the uplink STAs andmay inform the channel (or subchannel) information allocated to theuplink STAs. When the AP transmits the trigger frame, a plurality ofSTAs transmit uplink data through the respective allocated subcarriersat a time point designated by the trigger frame. After the uplink datatransmission is completed, the AP transmits an ACK to the STAs that havesuccessfully transmitted the uplink data. In this case, the AP maytransmit a predetermined multi-STA block ACK (M-BA) as an ACK for aplurality of STAs.

In the non-legacy wireless LAN system, a specific number, for example,26, 52, or 106 tones may be used as a resource unit (RU) for asubchannel-based access in a channel of 20 MHz band. Accordingly, thetrigger frame may indicate identification information of each STAparticipating in the multi-user uplink transmission and information ofthe allocated resource unit. The identification information of the STAincludes at least one of an association ID (AID), a partial AID, and aMAC address of the STA. Further, the information of the resource unitincludes the size and placement information of the resource unit.

On the other hand, in the non-legacy wireless LAN system, multi-useruplink transmission may be performed based on a contention of aplurality of STAs for a particular resource unit. For example, if an AIDfield value for a particular resource unit is set to a specific value(e.g., 0) that is not assigned to STAs, a plurality of STAs may attemptrandom access (RA) for the corresponding resource unit. Therefore, thereis a need for a method of allocating resources for a random access basedmulti-user uplink transmission of such a plurality of STAs.

FIGS. 8 and 9 illustrate a hidden node protection method in a multi-usertransmission process. In the multi-user uplink/downlink transmissionprocess, NAV setting of terminals not participating in data transmissionis required. In particular, when multi-user transmission is performed ona subchannel basis, there is a need for a method that enables legacyterminals that cannot receive subchannel data to correctly set the NAV.

FIG. 8 illustrates a hidden node protection method in a downlink OFDMA(DL-OFDMA) transmission. According to the embodiment of the presentinvention, an RTS and/or CTS frame of a predetermined format is used forNAV setting in the DL-OFDMA transmission process. First, the APtransmits a multi-user RTS (MU-RTS) frame 310 for NAV setting in theDL-OFDMA transmission process. The duration field of the MU-RTS frame310 is set to a value until the end of the DL-OFDMA session. That is,the duration field of the MU-RTS frame 310 is set based on a perioduntil the downlink data transmission of the AP and the ACK frametransmission of STAs are completed. Neighboring terminals of the AP seta NAV until the end of the DL-OFDMA session based on the duration fieldof the MU-RTS frame 310 transmitted by the AP. According to anembodiment, the MU-RTS frame 310 may be configured in the format of atrigger frame and requests transmissions of simultaneous CTS frames 320of the STAs.

The STAs (i.e., STA1 and STA2) receiving the MU-RTS frame 310 from theAP transmit a simultaneous CTS frame 320. The simultaneous CTS frame 320transmitted by a plurality of STAs has the same waveform. That is, thesimultaneous CTS frame 320 transmitted by the STA1 through the firstchannel has the same waveform as the simultaneous CTS frame 320transmitted by the STA2 through the first channel. According to anembodiment, the simultaneous CTS frame 320 is transmitted on the channelindicated by the MU-RTS frame 310. The duration field of thesimultaneous CTS frame 320 is set up to the point at which the DL-OFDMAsession is terminated based on the information of the duration field ofthe MU-RTS frame 310. That is, the duration field of the simultaneousCTS frame 320 is set based on a period until the downlink datatransmission of the AP and the ACK frame transmission of STAs arecompleted. In FIG. 8, the neighboring terminals of STA1 and STA2 set theNAV until the end of the DL-OFDMA session based on the duration field ofthe simultaneous CTS frame 320.

According to an embodiment of the present invention, the MU-RTS frame310 and the simultaneous CTS frame 320 may be transmitted on a 20 MHzchannel basis. Accordingly, neighboring terminals including the legacyterminals can receive the MU-RTS frame 310 and/or the simultaneous CTSframe 320 and set the NAV.

When the transmissions of the MU-RTS frame 310 and the simultaneous CTSframe 320 are completed, the AP transmits DL data frame 330. In FIG. 8,an embodiment that the AP transmits DL-OFDMA data to STA1 and STA2,respectively, is illustrated. The STAs receive the DL data frame 330transmitted by the AP and transmit an uplink ACK 340 in responsethereto.

FIG. 9 illustrates a hidden node protection method in an uplink OFDMA(UL-OFDMA) transmission. In the embodiment of FIG. 9, duplicativedescription of parts which are the same as or corresponding to theembodiment of FIG. 8 will be omitted.

According to the embodiment of the present invention, a protectionmethod similar to that of the DL-OFDMA transmission process may be usedin the UL-OFDMA transmission process. As described above, the UL-OFDMAtransmission process is started by a trigger frame. According to theembodiment of the present invention, the AP transmits an MU-RTS frame312 configured in the format of a trigger frame for NAV setting in theUL-OFDMA transmission process. The AP may indicate that thecorresponding frame is the MU-RTS frame 312 through a predeterminedfield of the trigger frame. The predetermined field is a fieldindicating a type of the trigger frame.

The duration field of the MU-RTS frame 312 transmitted by the AP is setto a value until the end of the UL-OFDMA session. That is, the durationfield of the MU-RTS frame 312 is set based on the period until theuplink data transmission of the STAs and the ACK frame transmission ofthe AP are completed. The neighboring terminals of the AP set a NAVuntil the end of the UL-OFDMA session based on the duration field of theMU-RTS frame 312 transmitted by the AP. As described above, according tothe embodiment of the present invention, the AP can increase anefficiency of the UL-OFDMA transmission process by transmitting theMU-RTS frame 312 in which the functions of the trigger frame areintegrated.

The STAs (i.e., STA1, STA2) receiving the MU-RTS frame 312 from the APtransmit a simultaneous CTS frame 322. As described above, thesimultaneous CTS frame 322 transmitted by a plurality of STAs has thesame waveform. The duration field of the simultaneous CTS frame 322 isset up to the point at which the UL-OFDMA session is terminated based onthe information of the duration field of the MU-RTS frame 312. That is,the duration field of the simultaneous CTS frame 322 is set based on aperiod until the uplink data transmission of the STAs and the ACK frametransmission of the AP are completed. The neighboring terminals of STA1and STA2 set a NAV until the end of the UL-OFDMA session based on theduration field of the simultaneous CTS frame 322.

Resource units are allocated to the STAs through the MU-RTS frame 312transmitted by the AP, and the STAs transmit UL data frames 332 throughthe allocated resource units. In FIG. 9, an embodiment that STA1 andSTA2 transmit UL-OFDMA data to the AP, respectively, is illustrated. TheAP receives UL data frames 332 transmitted by the STAs and transmits amulti-STA block ACK (M-BA, 342) in response thereto.

Meanwhile, the STAs being allocated the resource unit in the UL-OFDMAtransmission process transmit a simultaneous CTS frame 322 after SIFSfrom the reception of the MU-RTS frame 312, and transmit UL data frame332 after xIFS from the transmission of the simultaneous CTS frame 322.According to an exemplary embodiment, since the STAs that havetransmitted the simultaneous CTS frame 322 can transmit UL data withoutswitching transmission/reception, the xIFS can be set to a time shorterthan the SIFS.

FIG. 10 illustrates a structure of a trigger frame according to anembodiment of the present invention. The frame control field and theduration field are set according to a method defined in a conventionalwireless LAN frame. The transmitter address (TA) field indicates the MACaddress of the terminal (i.e., the AP) transmitting the trigger frame400. On the other hand, since the trigger frame 400 is transmitted to aplurality of receiving terminals, the receiver address (RA) field may beomitted or may indicate a predefined MAC address.

The trigger frame 400 includes a common information field 410 and a userinformation field 420. The common information field 410 indicatesinformation that is commonly applied to a plurality of STAs receivingthe trigger frame 400. More specifically, the common information field410 may include at least one of a protection field 412, an UL/DLindication field 414, a resource unit pattern field 416, and a resourceunit pattern bitmap field 418.

According to an embodiment, the protection field 412 indicates whetherthe corresponding trigger frame 400 is an MU-RTS frame. When theprotection field 412 is set to 1, the corresponding trigger frame 400 isan MU-RTS frame, and terminals receiving the trigger frame 400 set a NAVbased on the duration field of the corresponding trigger frame 400. Whenthe protection field 412 is set to 0, the trigger frame 400 is a basictrigger frame, and the trigger frame 400 is not used for NAV setting ofneighboring terminals.

In accordance with a further embodiment of the present invention, thetrigger frame 400 may have two or more types and the protection field412 may represent the type information of the trigger frame 400. In thiscase, one of the types of the trigger frame 400 may be an MU-RTS.

The UL/DL indication field 414 indicates whether the correspondingtrigger frame 400 triggers a multi-user uplink data transmission or amulti-user downlink data transmission. Transmission and receptionoperations of the terminals after the transmission of the trigger frame400 and the transmission of the simultaneous CTS frame may be performedbased on the UL/DL indication field 414. Although the UL/DL indicationfield 414 is illustrated in FIG. 10 as being included in the MAC headerof the trigger frame 400, the present invention is not limited thereto.According to another embodiment of the present invention, the UL/DLindication field may be included in the PHY preamble of the transmittedpacket, for example, HE-SIG-A. In this case, the UL/DL indication fieldmay indicate whether the corresponding packet is an uplink packet or adownlink packet.

Next, the resource unit pattern field 416 and the resource unit patternbitmap field 418 represent advance information for the user informationfield 420 having a variable size. According to the embodiment of thepresent invention, a plurality of resource unit patterns for assigningresource units to respective STAs can be predefined as described inFIGS. 11 and 12. Trigger frame 400 may deliver resource unit allocationinformation to STAs by designating a pattern number for a predefinedresource unit pattern.

The resource unit pattern is composed of a combination of at least oneresource unit, and each resource unit has a size of 26-tone, 52-tone or106-tone. According to an embodiment, each resource unit pattern may becomposed of at least three to at most nine resource units. If a patternnumber is designated in the resource unit pattern field 416, the triggerframe 400 may include user information fields 420 corresponding to thenumber of resource units included in the pattern. In this case, the AIDfield 422 for each user inserted in the user information field 420 issequentially corresponded to each resource unit of the correspondingresource unit pattern.

The resource unit pattern bitmap field 418 indicates information on aneffective resource unit in which the trigger frame 400 performsallocation among the resource units of the resource unit pattern.According to an embodiment, the AP may allocate only a certain number ofresource units among the plurality of resource units in the 20 MHzchannel to the STAs. When the resource unit pattern includes a maximumof nine resource units, the resource unit pattern bitmap field 418 maybe set to a size of nine bits.

The resource unit pattern bitmap field 418 may indicate whether or noteach resource unit is allocated to STAs in the order of the resourceunits constituting the resource unit pattern. For example, when aresource unit pattern including nine resource units is used and only asecond one of the resource units is allocated to a STA, the resourceunit pattern bitmap field 418 may be set to 010000000. In this case, thetrigger frame 400 may include a user information field 420 correspondingto the number of resource units allocated to the STA. That is, since onebit is activated in the resource unit pattern bitmap field 418, thetrigger frame 400 includes one user information field 420. As anotherexample, when a resource unit pattern including five resource units isused and a third and a fifth resource unit are allocated to STAs, theresource unit pattern bitmap field 418 may be set to 001010000. In thiscase, only the first five bits of the resource unit pattern bitmap field418 may be regarded as valid information. Since two bits are activatedin the resource unit pattern bitmap field 418, the trigger frame 400includes two user information fields 420.

Next, the user information field 420 indicates information applied to anindividual STA that receives the trigger frame 400. As described above,the trigger frame 400 may include the user information field 420 as manyas the number of resource units included in the specified resource unitpattern, or may include the user information field 420 as many as thenumber of resource units allocated to STAs. The user information field420 includes an AID field 422 corresponding to each resource unit. TheAID field 422 may indicate an AID of a STA to which the correspondingresource unit is assigned. According to another embodiment, the AIDfield 422 may represent a group AID or a temporary AID according tovarious embodiments described below.

FIG. 10 illustrates a structure of a trigger frame 400 according to anembodiment of the present invention. Some fields of the trigger frame400 illustrated in FIG. 10 may be omitted according to an embodiment. Inaddition, a specific field not illustrated in FIG. 10 may be furtherincluded in the trigger frame 400. The AP generates a trigger frame 400or an MU-RTS frame in this format, and transmits the frame to start amulti-user uplink transmission process or a multi-user downlinktransmission process.

FIG. 11 illustrates a configuration of a resource unit pattern accordingto an embodiment of the present invention. The resource unit patternconstituting a 20 MHz channel is constituted by a combination of atleast one resource unit, and each resource unit has a size of 26-tone,52-tone or 106-tone. According to an embodiment of the presentinvention, the central resource unit of the 20 MHz channel is fixed to asize of 26-tone. Both side resource units in reference to the centralresource unit may be configured as a combination of at least one of26-tone, 52-tone and 106-tone. In this case, 35 resource unit patternsas illustrated in FIG. 11 may be defined.

Pattern 1 consists of nine 26-tone resource units. In this case, amaximum of nine AIDs can be assigned to each resource unit. Patterns 2to 7 consist of one 52-tone resource unit and seven 26-tone resourceunits. In this case, a maximum of 8 AIDs can be assigned to eachresource unit. Patterns 8 to 18 consist of two 52-tone resource unitsand five 26-tone resource units. In this case, a maximum of 7 AIDs canbe assigned to each resource unit. Patterns 19 to 23 consist of three52-tone resource units and three 26-tone resource units. In this case, amaximum of six AIDs can be assigned to each resource unit. The pattern24 consists of four 52-tone resource units and one 26-tone resourceunit. In this case, a maximum of 5 AIDs can be assigned to each resourceunit.

Pattern 25 and pattern 30 consist of one 106-tone resource unit and five26-tone resource units. In this case, a maximum of six AIDs can beassigned to each resource unit. The patterns 26 to 28 and the patterns31 to 33 consist of one 106-tone resource unit, one 52-tone resourceunit, and three 26-tone resource units. In this case, a maximum of 5AIDs can be assigned to each resource unit. Pattern 29 and pattern 34consist of one 106-tone resource unit, two 52-tone resource units, andone 26-tone resource unit. In this case, a maximum of four AIDs can beassigned to each resource unit. The pattern 35 consists of two 106-toneresource units and one 26-tone resource unit. In this case, a maximum ofthree AIDs can be assigned to each resource unit.

FIG. 12 illustrates a configuration of a resource unit pattern accordingto another embodiment of the present invention. In the embodiment ofFIG. 12, duplicative description of parts which are the same as orcorresponding to the embodiment of FIG. 11 will be omitted.

When assigning STAs to each resource unit of a 20 MHz channel, resourceunit patterns can be simplified if frequency selectivity is notconsidered. According to the embodiment of FIG. 12, each resource unitof the resource unit pattern may be arranged in the order of size. Asdescribed above, the central resource unit of the 20 MHz channel isfixed to a size of 26-tone. Both side resource units in reference to thecentral resource unit may be configured as a combination of at least oneof 26-tone, 52-tone and 106-tone, and the both side resource units arearranged in the order of size. In this case, as illustrated in FIG. 12,a total of nine resource unit patterns can be defined.

Pattern 1 consists of nine 26-tone resource units. In this case, amaximum of nine AIDs can be assigned to each resource unit. Pattern 2consists of one 52-tone resource unit and seven 26-tone resource units.In this case, a maximum of 8 AIDs can be assigned to each resource unit.Pattern 3 consists of two 52-tone resource units and five 26-toneresource units. In this case, a maximum of 7 AIDs can be assigned toeach resource unit. Pattern 4 consists of three 52-tone resource unitsand three 26-tone resource units. In this case, a maximum of six AIDscan be assigned to each resource unit. Pattern 5 consists of four52-tone resource units and one 26-tone resource unit. In this case, amaximum of 5 AIDs can be assigned to each resource unit.

Pattern 6 consists of one 106-tone resource unit and five 26-toneresource units. In this case, a maximum of 7 AIDs can be assigned toeach resource unit. Pattern 7 consists of one 106-tone resource unit,one 52-tone resource unit, and three 26-tone resource units. In thiscase, a maximum of 5 AIDs can be assigned to each resource unit. Pattern8 consists of one 106-tone resource unit, two 52-tone resource units,and one 26-tone resource unit. In this case, a maximum of four AIDs canbe assigned to each resource unit. Pattern 9 consists of two 106-toneresource units and one 26-tone resource unit. In this case, a maximum ofthree AIDs can be assigned to each resource unit.

As described above, according to the embodiment of FIGS. 11 and 12, theresource unit pattern includes at least one 26-tone resource unit andcan be composed of at least three to at most nine resource units.According to the embodiment of FIG. 11, the resource unit pattern fieldmay have a size of 6 bits. On the other hand, according to theembodiment of FIG. 12, the resource unit pattern field can be simplifiedto a size of 4 bits. According to another embodiment of the presentinvention, a 106-tone resource unit may be replaced with a 102-toneresource unit or a 104-tone resource unit according to the arrangementof pilot subcarriers and data subcarriers.

FIG. 13 illustrates a structure of a common information field of atrigger frame according to another embodiment of the present invention.In the embodiment of FIG. 13, duplicative description of parts which arethe same as or corresponding to the embodiment of FIG. 10 will beomitted.

According to another embodiment of the present invention, the commoninformation field 410 of the trigger frame may further include afrequency selectivity field 415. In constructing the resource unitpattern, the frequency selectivity may be selectively reflectedaccording to the network environment. If the frequency selectivity isreflected as in the embodiment of FIG. 11, the length of the resourceunit pattern field 416 may be set to 6 bits. In addition, if thefrequency selectivity is not reflected as in the embodiment of FIG. 12,the length of the resource unit pattern field 416 may be set to 4 bits.The frequency selectivity field 415 indicates information on whichlength among the lengths of the variable resource unit pattern field 416is used. That is, the frequency selectivity field 415 indicates whichpattern set is to be used among the predetermined resource unit patternsets.

FIGS. 14 to 16 illustrate a temporary AID assignment method for amulti-user uplink transmission. According to an embodiment of thepresent invention, a temporary AID may be used for a particular resourceunit in the multi-user uplink transmission.

In a non-legacy wireless LAN system, a multi-user uplink transmissionmay be performed based on competition of a plurality of STAs for aparticular resource unit. For example, if an AID field value for aparticular resource unit is set to a particular value (e.g., 0) that isnot assigned to the STA, a plurality of STAs may attempt random access(RA) for the corresponding resource unit. Therefore, a method ofallocating resources for such a random access based multi-user uplinktransmission of a plurality of STAs is needed.

According to an embodiment, a probe request and/or an associationrequest may be transmitted through a random access based multi-useruplink transmission. That is, STAs that are not assigned an AID cantransmit a probe request or association request to the AP through aresource unit for random access in a multi-user uplink transmissionprocess. After the multi-user uplink transmission is completed, the APtransmits ACK information for the requests of the STAs through a blockACK. However, since STAs that have transmitted the requests to the APhave not been assigned an AID, a method for the STAs to identify ACKinformation for themselves in the block ACK is needed.

FIG. 14 illustrates a structure of a trigger frame and a resource unitpattern according to an embodiment of the present invention. FIG. 14illustrates an example of a temporary AID assignment method describedlater. FIG. 14 (a) illustrates a structure of a trigger frame, and FIG.14 (b) illustrates a resource unit pattern. In the embodiment of FIG.14, the same or corresponding parts as those of the embodiment of FIGS.10 to 13 are not described.

As described above, a plurality of resource unit patterns for assigningresource units to respective STAs can be predefined. The trigger framemay deliver resource unit allocation information to STAs by designatinga pattern number for a predefined resource unit pattern. In the OFDMA ofthe non-legacy wireless LAN system, resources are allocated in acombination of at least one of 26-tone, 52-tone and 106-tone resourceunits and pilots within a 242-tone available in a 20 MHz channel. Sincethe combination of resource units having fixed sizes is used, the numberof resource unit patterns may be finite, and pattern numbers for allcombination patterns can be assigned and designated. The trigger framemay designate a pattern number for identifying the corresponding one ofthe predefined resource unit patterns through the resource unit patternfield 416. In addition, the user information field 420 may designateAIDs sequentially corresponding to each resource unit of the resourceunit pattern through the AID field for each user.

For example, if the pattern number of the resource unit pattern consistof resource units of 106-tone, 26-tone, 52-tone, 26-tone and 26-tone isy and the resource units may be allocated as a sequence of (106-tone:STA1, 26-tone: STA2, 52-tone: STA3, 26-tone: STA4, 26-tone: STAS). Inthis case, the value of the resource unit pattern field 416 of thetrigger frame is set to ‘y’. In addition, AID fields for each user inthe user information field 420 of the trigger frame are sequentiallyinserted with AIDs corresponding to STA1, STA2, STA3, STA4 and STAS. Ifthe central resource unit of the 20 MHz channel is fixed to a size of26-tone, the size of the resource unit pattern field 416 may be set to 1byte. According to another embodiment, when the condition for patternallocation is mitigated, the size of the resource unit pattern field 416may be designated as 2 to 3 bytes. In addition, since the number of STAsallocated according to the resource unit pattern may vary, the structureof the user information field 420 may be variable.

FIG. 15 illustrates a resource allocation method for a random accessbased multi-user uplink transmission according to an embodiment of thepresent invention. In the embodiment of FIG. 15, it is assumed that thepattern 1 of FIG. 14 is allocated as the resource unit pattern of theprimary channel and the pattern y of FIG. 14 is allocated as theresource unit pattern of the secondary channel.

First, referring to FIG. 15 (a), the pattern 1 composed of nine 26-toneresource units is used in the primary channel. In this case, the firstresource unit, the fifth resource unit, and the seventh resource unitare allocated to STAs of AIDs 8, 26, and 278, respectively. Theremaining resource units, i.e., the second to fourth resource units, thesixth resource unit, and the eighth to ninth resource units are set asrandom access resource units. In the secondary channel, a pattern ycomposed of one 106-tone resource unit, one 52-tone resource unit andthree 26-tone resource units is used. In this case, the second resourceunit, the fourth resource unit, and the fifth resource unit areallocated to STAs of AIDs 574, 293, and 39, respectively. The remainingresource units, i.e., the first resource unit and the third resourceunit are set as random access resource units.

FIG. 15 (b) illustrates an embodiment of a method of representing a userinformation field of a trigger frame for the channel of FIG. 15 (a).According to an embodiment of the present invention, the AID field valueof the trigger frame indicating a random access resource unit may be setto 0. That is, when the AID field value of the trigger frame for aparticular resource unit is 0, STAs can attempt random access to thecorresponding resource unit. The STAs that have succeeded in randomaccess can receive ACK information through a block ACK transmitted bythe AP. However, when there are a plurality of resource units allocatedfor random access, each STA needs a method for identifying ACKinformation for the corresponding STA in the block ACK.

According to an embodiment of the present invention, a temporary AID maybe used to identify ACK information for each STA in the block ACK. In anembodiment of the present invention, the temporary AID is selected fromunused AIDs in the corresponding BSS. Thus, the temporary AID has adifferent value from the AIDs assigned to each STA in the BSS. In thewireless LAN system, a value selected from the range of 0 to 2007 can beused as an AID of the terminal, and the value after 2008 is not assignedto an AID of the terminal. That is, the first AID set consists of AIDsused for the AID assignment of the terminals, and the second AID setconsists of AIDs not used for the AID assignment of the terminals.According to an embodiment of the present invention, a temporary AID maybe selected from the second AID set. In this case, the first AID set mayinclude AIDs from 0 to 2007, and the second AID set may include AIDsafter 2008.

According to the embodiment of the present invention, the AP may assignsequentially increasing temporary AIDs to the random access resourceunits. When the resource unit pattern is determined, the number ofresource units constituting the pattern is determined, and temporaryAIDs corresponding to the determined number of resource units areassigned. According to an embodiment, the temporary AID may besequentially assigned from the second AID set.

Referring to FIG. 15 (b), temporary AIDs increasing one by one from 2008are assigned to the second to fourth resource units, the sixth resourceunit, and the eighth to ninth resource units, which are random accessresource units of the primary channel. In other words, 2008, 2009 and2010 are assigned to the second to fourth resource units, 2011 isassigned to the sixth resource units, and 2012 and 2013 are assigned tothe eighth to ninth resource units, respectively. When UL-OFDMA isperformed through a plurality of channels, the temporary AID used forthe block ACK may be assigned a different value for each channel.Alternatively, the temporary AID may be assigned independently for eachchannel. In other words, according to an embodiment, 2013 and 2015,which are values after the temporary AID assigned to the primarychannel, may be assigned to the first resource unit and the thirdresource unit, which are the random access resource units of thesecondary channel, respectively. According to another embodiment, 2008and 2009 may be assigned to the temporary AIDs of the first resourceunit and the third resource unit of the secondary channel, respectively,independently from the primary channel.

FIG. 15 (c) illustrates another embodiment of the method of representingthe user information field of the trigger frame for the channel of FIG.15 (a). According to the embodiment of FIG. 15 (c), the AID field valueof the trigger frame indicating the random access resource unit may beset to the temporary AID value determined as described above.

The AP transmits ACK information to each STA through a block ACK usingthe temporary AID selected as described above. Meanwhile, theabove-described temporary AID selection method is an embodiment of thepresent invention, and the present invention is not limited thereto.According to another embodiment of the present invention, the temporaryAID may be selected from the first AID set as well as the second AIDset. That is, unused AIDs which are not assigned to STAs of thecorresponding BSS in the first AID set can be selected as temporaryAIDs.

If the probe request or the association request is transmitted throughthe random access resource unit, the AP can further assign a real AID bytransmitting a probe response or an association response to thecorresponding STA. According to another embodiment of the presentinvention, when a STA to which the AID is already assigned performs themulti-user uplink transmission using the random access resource unit,the AP may deliver ACK information of the block ACK using the AIDassigned to the corresponding STA.

FIG. 16 illustrates a resource allocation method for random access basedmulti-user uplink transmission according to another embodiment of thepresent invention. In the embodiment of FIG. 16, duplicative descriptionof parts which are the same as or corresponding to the embodiment ofFIG. 15 will be omitted.

First, referring to FIG. 16 (a), the resource unit configuration of theprimary channel is the same as that of FIG. 15 (a). However, even in thesecondary channel, pattern 1 composed of nine 26-tone resource units isused, and all resource units are set as random access resource units.

The trigger frame and the block ACK used in the multi-user uplinktransmission process have a variable length according to the number ofallocated STAs. In order to provide an efficient frame transmission andprevent collision with operation of the legacy wireless LAN system, itis desirable to use a frame as short as possible. According to anembodiment of the present invention, a temporary AID indication methodfor reducing the length of a trigger frame supporting random access maybe used.

Referring to FIG. 16 (b), a designated AID is assigned to the firstresource unit of the primary channel, and the second through fourthresource units are set as random access resource units. In this case, itis possible to consecutively assign 2008, 2009, and 2010 as temporaryAIDs to the second to fourth resource units. In this case, in order toreduce the length of the trigger frame, only the 2010, which is thelargest value among the consecutively assigned temporary AID values, maybe inserted into the AID field of the trigger frame, and therepresentation of 2008 and 2009 may be omitted. The STAs receiving thetrigger frame can attempt random access on total three resource units byinversely estimating that the two temporary AIDs are omitted whenobtaining 2010 as the temporary AID value for the second resource unit.A designated AID is assigned to the fifth resource unit of the primarychannel, and the sixth resource unit is set to the random access unit.In this case, since there is no continuous random access resource unit,a temporary AID 2011 is inserted into the AID field of the trigger frameas in the conventional method. It is possible to assign a designated AIDto the seventh resource unit of the primary channel and consecutivelyassign 2012 and 2013 as temporary AIDs to the eighth to ninth resourceunits. In this case, only 2013, which is the largest value among theconsecutively assigned temporary AID values, may be inserted into theAID field of the trigger frame, and the representation of 2012 may beomitted.

When all nine resource units are set as the random access resource unitssuch as the secondary channel of FIG. 16 (b), only the maximum valueamong the consecutive temporary AIDs may be inserted into the AID fieldof the trigger frame. If the temporary AID is assigned as a differentvalue for each channel, the maximum value 2022 among the temporary AIDs2014 to 2022 may be inserted in the AID field of the trigger frame. Ifthe temporary AID is assigned independently for each channel, 2016,which is the maximum value among the temporary AIDs of 2008 to 2016, maybe inserted in the AID field of the trigger frame. By inserting themaximum value among the temporary AIDs in the assignable range into theAID field of the trigger frame, the AP can inform the STAs that a totalof nine random access resource units have been set.

FIGS. 17 and 18 illustrate a method for multi-user uplink transmissionusing a temporary AID assignment method according to the above-describedembodiments. According to the embodiment of FIGS. 17 and 18, thetemporary AID may be specified to the STAs via the trigger frame and maybe used for identifying ACK information of the block ACK correspondingto the multi-user uplink transmission.

FIG. 17 illustrates an embodiment in which an OFDMA block ACK istransmitted in response to the multi-user uplink transmission. The APtransmits a trigger frame 400 that triggers a multi-user uplink datatransmission, and STAs receive the trigger frame 400. As describedabove, the trigger frame 400 includes a common information field 410 anduser information fields 420, and an AID field value of at least one ofthe user information fields 420 may be set to a temporary AID. The STAsmay obtain the temporary AID from the received trigger frame 400.

The STAs receiving the trigger frame 400 transmit multi-user uplink data500 in response thereto. Each STA selects at least one resource unitamong the resource units specified by the trigger frame to transmit themulti-user uplink data 500. In this case, the resource unit on which themulti-user uplink data 500 is transmitted may include a random accessresource unit. In addition, the temporary AID of the above-describedembodiments may be assigned to at least one resource unit on which themulti-user uplink data 500 is transmitted.

The AP receives the multi-user uplink data 500 transmitted by the STAsand transmits an OFDMA block ACK 600 in response thereto. The STAs thattransmitted the multi-user uplink transmission data 500 receive theOFDMA block ACK 600. According to an embodiment of the presentinvention, a STA may obtain ACK information for the corresponding STAwithin the OFDMA block ACK 600 based on the temporary AID. According toan embodiment, an HE-SIG-B of the OFDMA block ACK 600 may includetemporary AID information assigned to at least one resource unit.

The STAs identify the ACK information in the OFDMA block ACK 600 basedon the temporary AID of the resource unit on which the multi-user uplinkdata 500 transmission is performed. A plurality of STAs may transmit themulti-user uplink data 500 on the same resource unit corresponding tothe same temporary AID. Accordingly, the STAs check ACK information ofthe resource unit corresponding to the temporary AID of the STAs in theOFDMA block ACK 600, and check whether a MAC address of the ACKinformation matches a MAC address of the corresponding STA. If the MACaddress of the ACK information matches the MAC address of the STA, theSTA determines that the transmission of the multi-user uplink data 500is successful. However, if the MAC address of the ACK information doesnot match the MAC address of the STA, the STA determines that thetransmission of the multi-user uplink data 500 has failed.

As described above, according to the embodiment of the presentinvention, the temporary AID may indicate the resource unit containingACK information for each STA in the OFDMA block ACK 600. In this case,the temporary AID may be a group AID corresponding to a plurality ofSTAs performing the transmission of the multi-user uplink data 500.

FIG. 18 illustrates an embodiment in which a multi-STA block ACK (M-BA)is transmitted in response to the multi-user uplink transmission. In theembodiment of FIG. 18, duplicative description of parts which are thesame as or corresponding to the embodiment of FIG. 17 will be omitted.

The AP transmits a trigger frame 400 as described above, and the STAsreceive the trigger frame 400. The STAs may obtain a temporary AID fromthe received trigger frame 400. The STAs receiving the trigger frame 400transmit multi-user uplink data 520 in response thereto. A temporary AIDof the above-described embodiment may be assigned to at least oneresource unit on which the multi-user uplink data 520 is transmitted.

The AP receives the multi-user uplink data 520 transmitted by the STAsand transmits a corresponding M-BA 620 in response thereto. The STAsthat have transmitted the multi-user uplink transmission data 520receive the M-BA 620. According to an embodiment of the presentinvention, the STA may obtain ACK information for the STA in the M-BA620 based on the temporary AID. According to an embodiment, the per-STAinformation field of the M-BA 620 may include temporary AID informationassigned to at least one resource unit.

The STAs identify ACK information in the M-BA 620 based on the temporaryAID of the resource unit on which the transmission of the multi-useruplink data 520 is performed. A plurality of STAs may transmit themulti-user uplink data 520 on the same resource unit corresponding tothe same temporary AID. Accordingly, the STA checks a per-STAinformation field corresponding to the temporary AID of the STA in theM-BA 620 and checks whether a MAC address of the per-STA informationfield matches a MAC address of the corresponding STA. If the MAC addressof the per-STA information field matches the MAC address of the STA, theSTA determines that the transmission of the multi-user uplink data 520is successful. However, if the MAC address of the per-STA informationfield does not match the MAC address of the STA, the STA determines thatthe transmission of the multi-user uplink data 520 has failed.

Hereinafter, a random access based multi-user uplink transmission methodaccording to another embodiment of the present invention will bedescribed with reference to FIG. 19 to FIG. 21.

In a non-legacy wireless LAN system, STAs attempting UL-OFDMA randomaccess compete to obtain transmission opportunities. The STAs select arandom number within a predetermined range as an OFDMA BackOff (OBO)counter, and perform a random access based on the selected OBO counter.STAs decrease their OBO counter by the number of resource unitsallocated for random access in every time a trigger frame istransmitted. That is, when N resource units are allocated for the randomaccess, the STAs can reduce the OBO counter by a maximum of N in onecompetition process. STAs whose OBO counter value is smaller than orequal to the number of resource units currently allocated for randomaccess can perform a random access. The STAs arbitrarily select aresource unit allocated for the random access to perform a random accesstransmission. A STA that has not obtained a random access opportunity inthe contention process may attempt a random access by repeating the OBOcounter reduction process described above when the next trigger frame istransmitted.

According to the embodiment of the present invention, a control methodfor preventing excessive collision when a random access based multi-useruplink transmission is performed in a network congestion situation maybe used. For example, STAs having an OBO counter value smaller than orequal to the number of resource units currently allocated for randomaccess may perform an additional control process before attempting arandom access. Table 1 represents a random access control methodaccording to an embodiment of the present invention.

TABLE 1 Management P0 AC_VO P1 AC_VI P2 AC_BE P3 AC_BK P4

Here, P0>P1>P2>P3>P4.

In the Table 1, each item indicates an access category classified basedon the priority of data and a corresponding transmission probability.AC_VO indicates a voice access category, AC_VI indicates a video accesscategory, AC_BE indicates a best effort access category, and AC_BKindicates a background access category.

According to the embodiment of the present invention, STAs attempting arandom access may perform a differential access by assigning differentprobability values according to access categories of data to betransmitted. That is, STAs that have acquired the random accesstransmission opportunity perform the random access transmission with adesignated probability according to the access category of the data tobe transmitted by the corresponding terminal. The random accesstransmission probability of the STA having data of an access categorywith a high probability value becomes higher. When a trigger frameindicating a random access is received, the STAs determine whether toperform a random access based on a probability determined according toan access category of data in a buffer of the corresponding terminal.

According to a further embodiment, the AP may transmit a congestionprobability P_c with a value between 0 and 1 via the trigger frame. Asthe number of terminals in the BSS or the traffic increases, thecollision probability of the random access may be increased. The STAsthat have received the trigger frame perform the random accesstransmission based on the multiplication of a probability P determinedaccording to the access category and a congestion probability P_c set bythe AP. The congestion probability P_c may be set to a lower value asthe traffic in the BSS is higher. The AP can set the P_c value inconsideration of the number of collisions in the single-user (SU) andmulti-user (MU) transmission up to the present time. In addition,multi-user uplink transmission STAs sharing the same 20 MHz band arerequired to transmit L-SIG parts in duplicate in the non-legacy wirelessLAN system. Accordingly, the AP can estimate how many STAs haveattempted to transmit when every random access multi-user uplinktransmission is performed. The AP may set the P_c value by using suchadditional information together.

According to another embodiment, each STA may perform the random accesstransmission using a transmission probability table indexed by an accesscategory of data and congestion. The AP may transmit congestion indexinformation corresponding to the congestion probability P_c instead oftransmitting the congestion probability P_c. The STA may select thetransmission probability in the table based on the received congestionindex information and the access category information. The congestioninformation according to the above-described embodiments may be insertedinto the common information field of the trigger frame.

FIG. 19 illustrates a method of controlling a random access basedmulti-user uplink transmission according to a further embodiment of thepresent invention. In FIG. 19, a square box represents an existingaccess terminal, and a circular box represents a new access terminal.Also, a solid line box indicates a terminal performing random accesstransmission, and a dotted box indicates a terminal that suspends randomaccess transmission based on the above-described transmissionprobability. In the embodiment of FIG. 19, it is assumed that the numberof random access resource units is set to six.

First, FIG. 19 (a) illustrates a situation in which seven STAs have OBOcounters of six or less while six resource units are selected as randomaccess resource units. The seven STAs select random resource units amongthe six random access resource units to perform random accesstransmission. Since the number of STAs performing random accesstransmission is greater than the number of random access resource units,a collision occurs in at least one resource unit.

FIG. 19 (b) illustrates a situation in which STAs perform random accesstransmission based on the transmission probability of theabove-described embodiment. Each STA selects a transmission probabilitybased on at least one of an access category and congestion, anddetermines whether to perform a random access transmission based on theselected transmission probability. In the example of FIG. 19 (b), threeof the seven STAs with OBO counters of less than six have decided tosuspend the random access transmission. Therefore, the remaining fourSTAs perform the random access transmission through the six randomaccess resource units, and the collision probability of the randomaccess transmission is lowered.

FIGS. 19 (c) and 19 (d) illustrate situations in which random accesstransmission using OBO scaling is performed according to a furtherembodiment of the present invention. According to an embodiment, the APmay transmit a scaling factor to be used for random access via thetrigger frame. The STAs participating in the random access may use avalue obtained by multiplying the original OBO counter of thecorresponding terminal by the scaling factor as a new OBO counter. TheSTAs may use the scaled OBO counter as is, or may approximate thenearest integer value to determine the final OBO counter.

The OBO scaling method may reduce or increase the random access attemptrate of STAs. If there are many empty resource units in which the randomaccess transmission has not been performed in the previous multi-useruplink transmission, the AP may decrement the scaling factor to a valueof 1 or less, thereby increasing the number of STAs attempting randomaccess in the corresponding multi-user uplink transmission. In contrast,if there are many resource units in which a collision occurred in theprevious multi-user uplink transmission, the AP may increase the scalingfactor to a value of 1 or more, thereby reducing the number of STAsattempting random access in the corresponding multi-user uplinktransmission.

FIG. 19 (c) illustrates a situation where the scaling factor is set to0.5. Existing access terminals with previously OBO counters of 0, 1, 3,4, 7 and 9 will have the final OBO counters of 0, 0, 1, 2, 3 and 4respectively after an adjustment. Also, new access terminals withpreviously OBO counters of 1, 2, 5 and 8 will have final OBO counters of0, 1, 2 and 4 respectively after an adjustment. Based on these adjustedOBO counters, a total of 10 STAs with OBO counters of less than sixperform the random access transmission.

FIG. 19 (d) illustrates a situation where the scaling factor is set to2. Existing access terminals with previously OBO counters of 0, 1, 3, 4,7 and 9 will have the final OBO counters of 0, 2, 6, 8, 14 and 18respectively after an adjustment. In addition, new access terminals withpreviously OBO counters of 1, 2, 5 and 8 will have final OBO counters of2, 4, 10 and 16 respectively after an adjustment. Based on theseadjusted OBO counters, a total of four STAs with OBO counters of lessthan six perform the random access transmission.

According to the embodiment of the present invention, the scaling factormay be calculated on the basis of transmission records up to theprevious point, as well as the above-mentioned congestion probabilityP_c. The scaling factor may be inserted into the common informationfield of the trigger frame and transmitted to each STA.

FIG. 20 illustrates a buffer status reporting method using a randomaccess based multi-user uplink transmission according to an embodimentof the present invention.

In order to select multi-user uplink transmission STAs, the AP shouldidentify buffer status information of the STAs in advance. In thenon-legacy wireless LAN system, the AP may designate STAs through thetrigger frame to induce to transmit buffer status report. In addition,even if the STA is not induced by the trigger frame, the STA having anuplink opportunity to the AP may transmit the buffer status reporttogether with uplink data. The buffer status information is insertedinto a QoS control field of the MAC header to be transmitted to the AP.However, STAs that are neither designated by the AP nor have uplinktransmission opportunity to the AP cannot transmit buffer statusinformation.

According to an embodiment of the present invention, a plurality of STAsmay perform buffer status report transmission using random access basedmulti-user uplink transmission. Since the trigger frame for the randomaccess buffer status report targets a plurality of unspecified STAs, anAID field of the user information field of the trigger frame may be setto a predefined AID value. The predefined AID may be an AID designatedfor the random access buffer status report. Alternatively, an AIDindicating a random access based multi-user uplink transmission may beused as the predefined AID.

If the trigger frame only triggers the random access buffer statusreport, the duration field is set based on the length of the QoSdata/null frame according to a specific modulation and coding scheme(MCS). Since the AP may not know the channel conditions of the STAstransmitting the random access buffer status report in advance, the MCSof the trigger frame may be set to the lowest MCS or may be set to theMCS predefined for the random access buffer status report. The bufferstatus reports transmitted by a plurality of STAs may have the same datasize, and a resource unit pattern for a random access buffer statusreport may be composed of resource units of the smallest unit.

STAs receiving the trigger frame may identify the trigger of the randomaccess buffer status report based on the predefined AID or the durationfield value. STAs having uplink data transmit a buffer status reportthrough any resource unit. The buffer status report may be transmittedin QoS data/null format. According to a further embodiment of thepresent invention, a 1-bit identifier for the random access bufferstatus report may be inserted in the common information field of thetrigger frame for identification of the trigger frame for the randomaccess buffer status report.

FIG. 21 illustrates a buffer status reporting method using a randomaccess based multi-user uplink transmission according to anotherembodiment of the present invention. According to the embodiment of FIG.21, the buffer status report may be transmitted together with the uplinkdata.

The AP may configure the entire channel as resource units for reportingthe random access buffer status or may form a channel by mixing resourceunits for the random access buffer status report and resource units foruplink data transmission. When the random access buffer status report istransmitted together with the uplink data, the transmission duration mayvary depending on the MCS and the data size of the uplink data.Therefore, the duration field of the trigger frame may be set based onthe longest uplink data transmission length.

The STAs transmitting the random access buffer status report selectivelytransmit uplink data in the buffer based on the duration fieldinformation of the trigger frame. In this case, the STA may transmituplink data of the buffer by fragmenting the data based on the durationfield information of the trigger frame. If a random access buffer statusreport is triggered with uplink data, a predefined AID may be used toidentify it or an additional 1-bit identifier may be inserted into everyuser information field.

Although the present invention is described by using the wireless LANcommunication as an example, the present invention is not limitedthereto and the present invention may be similarly applied even to othercommunication systems such as cellular communication, and the like.Further, the method, the apparatus, and the system of the presentinvention are described in association with the specific embodiments,but some or all of the components and operations of the presentinvention may be implemented by using a computer system having universalhardware architecture.

The detailed described embodiments of the present invention may beimplemented by various means. For example, the embodiments of thepresent invention may be implemented by a hardware, a firmware, asoftware, or a combination thereof.

In case of the hardware implementation, the method according to theembodiments of the present invention may be implemented by one or moreof Application Specific Integrated Circuits (ASICSs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, micro-controllers, micro-processors,and the like.

In case of the firmware implementation or the software implementation,the method according to the embodiments of the present invention may beimplemented by a module, a procedure, a function, or the like whichperforms the operations described above. Software codes may be stored ina memory and operated by a processor. The processor may be equipped withthe memory internally or externally and the memory may exchange datawith the processor by various publicly known means.

The description of the present invention is used for exemplification andthose skilled in the art will be able to understand that the presentinvention can be easily modified to other detailed forms withoutchanging the technical idea or an essential feature thereof. Thus, it isto be appreciated that the embodiments described above are intended tobe illustrative in every sense, and not restrictive. For example, eachcomponent described as a single type may be implemented to bedistributed and similarly, components described to be distributed mayalso be implemented in an associated form.

The scope of the present invention is represented by the claims to bedescribed below rather than the detailed description, and it is to beinterpreted that the meaning and scope of the claims and all the changesor modified forms derived from the equivalents thereof come within thescope of the present invention.

INDUSTRIAL APPLICABILITY

Various exemplary embodiments of the present invention have beendescribed with reference to an IEEE 802.11 system, but the presentinvention is not limited thereto and the present invention can beapplied to various types of mobile communication apparatus, mobilecommunication system, and the like.

1-20. (canceled)
 21. A wireless station (STA), the STA comprising: atransceiver; and a processor, wherein the processor is configured to:receive a trigger frame for allocating one or more resources to at leastone STA from an AP (Access Point), and transmit a frame through aresource allocated to the STA among the one or more resources, whereinthe trigger frame includes an one or more AID (association identifier)field including an AID for allocating the one or more resources to theat least one STA, wherein the AID is set to a specific value or a valueselected from values in a specific range, wherein the values of thespecific range are used to allocate resources to STAs associated withthe AP, and wherein the specific value is used to allocate resources forrandom access to STAs not associated with the AP.
 22. The STA of claim21, wherein the specific range is from ‘0’ to ‘2007’.
 23. The STA ofclaim 21, wherein the processor is further configured to: receive an ACK(acknowledgment) frame in response to the frame from the AP, wherein theAck frame includes Ack information for some or all of the one or moreSTAs.
 24. The STA of claim 23, wherein the resource is indicated by anAID included in an AID field corresponding to the STA among the one ormore AID fields, and wherein the Ack information is identified from theAck frame based on the AID.
 25. The STA of claim 24, wherein the ACKframe is a multi-STA block ACK (M-BA) frame, and wherein the AID isincluded in an information field of the M-BA frame.
 26. The STA of claim21, wherein the specific value indicates at least one resource foruplink orthogonal frequency division multiple access (UL-OFDMA) based onthe random access among the one or more resources.
 27. The STA of claim26, wherein an OFDMA backoff (OBO) counter is used for UL-OFDMA based onthe random access.
 28. The STA of claim 27, wherein the OBO counter isdecremented based on a number of resource units indicated by thespecific value, when an AID for indicating the resource is set to thespecific value.
 29. A wireless communication method of a wirelesscommunication STA, the method comprising: receiving a trigger frame forallocating one or more resources to at least one STA from an AP (AccessPoint), and transmitting a frame through a resource allocated to the STAamong the one or more resources, wherein the trigger frame includes anone or more AID (association identifier) field including an AID forallocating the one or more resources to the at least one STA, whereinthe AID is set to a specific value or a value selected from values in aspecific range, wherein the values of the specific range are used toallocate resources to STAs associated with the AP, and wherein thespecific value is used to allocate resources for random access to STAsnot associated with the AP.
 30. The STA of claim 29, wherein thespecific range is from ‘0’ to ‘2007’.
 31. The STA of claim 29, whereinthe method is further configured to: receiving an ACK (acknowledgment)frame in response to the frame from the AP, wherein the Ack frameincludes Ack information for some or all of the one or more STAs. 32.The STA of claim 31, wherein the resource is indicated by an AIDincluded in an AID field corresponding to the STA among the one or moreAID fields, and wherein the Ack information is identified from the Ackframe based on the AID.
 33. The STA of claim 32, wherein the ACK frameis a multi-STA block ACK (M-BA) frame, and wherein the AID is includedin an information field of the M-BA frame.
 34. The STA of claim 29,wherein the specific value indicates at least one resource for uplinkorthogonal frequency division multiple access (UL-OFDMA) based on therandom access among the one or more resources.
 35. The STA of claim 34,wherein an OFDMA backoff (OBO) counter is used for UL-OFDMA based on therandom access.
 36. The STA of claim 34, wherein the OBO counter isdecremented based on a number of resource units indicated by thespecific value, when an AID for indicating the resource is set to thespecific value.